Metal functionally graded gyroids: additive manufacturing, mechanical properties, and simulation

Functionally graded materials raise considerable interest in the biomedical research. In particular, gyroid structures are suitable for bone tissue engineering applications, allowing to emulate the porosity of the inner part of the bone. In this frame, the mechanical properties of 17–4 PH steel gyroids made by additive manufacturing have been investigated. Three design methods have been implemented, i.e., thickness graded, size graded, and uniform, to address the lack of knowledge in the area of stainless-steel scaffolds aiming at providing a map of the mechanical properties. Compressive mechanical properties absorbed energy and absorption efficiency have been found for the aforementioned design methods. Furthermore, defects and collapse behavior have been analyzed: imperfections have been detected in the thin-walled areas of the graded samples. Nevertheless, under given conditions, the graded samples have mechanical properties comparable to those of uniform ones, exhibiting a controlled layer-by-layer collapse mechanism and consequent weight reduction. The Gibson-Ashby models have been implemented, and the calibration coefficients have been compared with other research works. A FEM-based numerical model has been proposed to reproduce the mechanical properties of the mentioned structures finding critical issues in the representation of defects. In this frame, the resulting Gibson Ashby calibration coefficients are in good agreement with the literature and reveal the graded samples have a bending-dominating behavior sustaining larger strains than the uniform case, giving the ground for high energy absorption applications. Furthermore, the FEM analyses are in good agreement with the literature providing a reliable tool to further investigate the metal functionally graded gyroid field.